1. Field of the Invention
The present invention relates to an apparatus and method for interference cancellation in a multiple-antenna communication system. More particularly, the present invention relates to interference cancellation in which a multiple-symbol processing scheme or a single-symbol processing scheme is selected according to a type of an interference signal in a receiver of an Orthogonal Frequency Division Multiple Access (OFDMA)-based multiple-antenna communication system.
2. Description of the Related Art
In general, wireless telecommunication systems provide data services in addition to voice services. To provide a data service with excellent performance, it is necessary to develop a high-speed data communication technology. A system channel capacity can significantly increase in a Multiple Input Multiple Output (MIMO) communication system in which both a transmitter and a receiver use multiple antennas.
Various well-known conventional technologies are used where both the transmitter and the receiver use multiple antennas. Examples of the techniques include Space Time Block Coding (STBC) which is performed by the transmitter to transmit signals through the multiple antennas, whereas the receiver detects the signals received through the multiple antennas according to a multiple-symbol processing scheme, and an interference cancellation technique.
In a communication system, a receiver (i.e., Mobile Station (MS)) may receive a signal from not only a desired transmitter (i.e., a Base Station (BS) located in a serving cell in which the receiver is located), but also an undesired transmitter (i.e., a BS located in a cell neighboring to the serving cell). In this case, a signal received by the receiver includes an undesired signal transmitted from the undesired transmitter as interference. Since the communication system experiences performance deterioration in the presence of interference, the interference has to be canceled in order to improve the performance of the communication system.
That is, in the communication system, when a receiver using multiple antennas receives an undesired signal (i.e., a signal received from an undesired transmitter), interference occurs to a desired signal (i.e., a signal received from a desired transmitter). In this case, the interference has to be canceled in order to prevent performance deterioration.
On the other hand, in a cellular communication system, when a receiver (i.e., MS) uses multiple antennas, a transmitter (i.e., BS) located in each cell may optionally use either multiple antennas or a single antenna.
A receiver using multiple antennas may receive a signal in two manners. First, the receiver receives a desired signal from a transmitter using a single antenna. Second, the receiver receives the desired signal from a transmitter using multiple antennas. In either case, it may not be effective to use the same interference cancellation scheme if an undesired signal is received from the transmitter using the single antenna and located in a neighboring cell (i.e., in the case of using one logical stream), as for the first case, and if the undesired signal is received from the transmitter using the multiple antennas and located in the neighboring cell, as for the second case.
In particular, interference becomes a big problem if several symbols are correlated, for example, when interference signals (i.e., undesired signals) received from the transmitter located in the neighboring cell are in association with multiple logical streams (e.g., Space-time Block Code (STBC) signals) transmitted from a transmitter having multiple antennas.
FIG. 1 is a graph illustrating a system performance of a receiver using multiple antennas in the presence of one-logical-stream type interference and multiple-logical-stream type interference. The graph shows that the performance deteriorates in the presence of the multiple-logical-stream type interference. Herein, the communication system is a Single Input Multiple Output (SIMO) system including a transmitter using one antenna and a receiver using five antennas. In the graph, a case where a transmitter located in a neighboring cell uses one antenna is indicated by SIMO, and a case of using multiple antennas is indicated by STBC. Symbols are detected by using Minimum Mean Squared Error (MMSE) scheme.
Accordingly, an apparatus and method for canceling interference caused by an undesired signal are required whereby, when a receiver using multiple antennas is located in an edge of a cell in a communication system, the interference is canceled if a desired signal is received from a transmitter located in the cell. The cancellation technique differs between a case where the undesired signal is received from a transmitter located in a neighboring cell using one antenna from and a case where the undesired signal is received from a transmitter located in the neighboring cell using multiple antennas.
In addition, an apparatus and method for canceling interference caused by an undesired signal are required, whereby, when a receiver using multiple antennas is located in an edge of a cell in a communication system, the interference is canceled. The cancellation technique differs between a case where a desired signal is received from a transmitter located in the cell using one antenna and a case where the desired signal is received from a transmitter located in the cell and using multiple antennas.